Inconsistent carbon and nitrogen isotope fractionation in the biotransformation of atrazine by Ensifer sp. CX-T and Sinorihizobium sp. K

Abstract Compound-specific stable isotope analysis (CSIA) has been used to quantify and identify biodegradation of organic pesticides in the environment. In this work, the kinetic isotope fractionation of carbon and nitrogen was investigated during rapid atrazine degradation by two bacterial isolates, CX-T ( Ensifer sp.) and K ( Sinorihizobium sp.), under aerobic conditions. Significant isotope fractionation (e carbon  = -2.40 ± 0.07‰, e nitrogen  = 1.30 ± 0.13‰, strain CX-T; e carbon  = -1.40 ± 0.07‰, e nitrogen  = 2.5 ± 0.5‰, strain K) was observed for both isolates. The same pattern of normal carbon and inverse nitrogen isotope effects were obtained, confirming the same reaction mechanisms of atrazine. The calculated, apparent kinetic isotope effects of strain CX-T (AKIE carbon  = 1.020; AKIE nitrogen  = 0.994) and strain K (AKIE carbon  = 1.011; AKIE nitrogen  = 0.988) were observed, implying that carbon-chlorine bonds weakened and additional bonds appeared on the triazine ring nitrogen at the transition state. However, isotope enrichment factors and dual isotope slopes (Δ =  δ 15 N/ δ 13 C) of both isolates (Δ = -0.55 ± 0.05, strain CX-T; Δ = -1.07 ± 0.14, strain K) were, nevertheless, inconsistent even for the same compound and same transformation pathway.